Nonreciprocal wave guide junction



Feb. 26, 1963 E. J. HlcKEY 3,079,570

NoNREcIPRocAL WAVE GUIDE JUNCTION Filed Jan. 25, 1961 ifa/wy 3,079,570NNRECLBRGCAL WAVE GUDE JUN'CTN Edward .lohn Hickey, Union, Nd., assignerto Airtron, Inc., Morris Plains, NJ.

Filed lian. 25, 1961, Ser. No. 84,822 1 Ciaim. (Cl. S33-1.1)

This invention relates to wave guide junctions and more particularly, tononreciprocal junctions employing ferromagnetic materials.

Wave guide junctions are well-known in the microwave field. Typicalreciprocal junctions are shown in page 234 of text entitled Principlesand Applications of Waveguide Transmission by George C. Southworth, D.Van Nostrand Co., Inc., New York, 1950. Nonreciprocal wave guideconnections or junctions were first disclosed in an article entitled TheFerromagnetic Faraday Effect at Microwave Frequencies and ItsApplications, subtitled The Microwave Gyrator, by C. L. Hogan, publishedin Bell System Technical Journal, Vol. 31, pp. 1-31, January 1952. Manyforms of nonreciprocal junctions have been proposed since that time.However, these junctions are often relatively complex and are normallyfixed in the nature of the switching action which is employed.

Accordingly, a principal object of the present invention is to provide asimple nonreciprocal wave guide junction in which the coupling betweenthe wave guides can readily be switched.

Another object of the present invention is to eliminate the need for abiasing current in a nonreciprocal wave guide junction switch.

In accordance with the present invention, the foregoing objects areachieved through the use of a cylinder of ferromagnetic material locatedin the junction of the wave guides. In accordance with one specificembodiment of the invention, a T wave guide junction is formed by theintersection of two Wave guides along the narrower side Wall of one ofthe guides. The cylinder of ferrite is located within the junctionopposite the branch wave guide connection. It may, for example, bemounted in position by transparent dielectric material such as polyfoam.A single copper wire may extend through the cylinder and the walls ofthe wave guide to a suitable pulse source, to selectively reverse themagnetic polarization of the ferrite cylinder.

The cylindrical form of the ferromagnetic element has the advantage thatit is readily permanently magnetized to a high level. Thus, with a briefpulse of approximately one microsecond duration applied through thesingle turn, microwave energy may be switched from one mode oftransmission through the junction to another. Because of theadvantageous geometry provided by a cylinder, the residual magneticforce present in the structure after the switching pulse is sutncient tomaintain the desired nonreciprocal action.

The novel features which are believed to be characteristic of theinvention both as to its organization and method of construction andoperation, together with further objects and advantages thereof, will bebetter understood from the following description when taken inconnection with the accompanying drawing in which an illustrativeembodiment of the invention is disclosed by way of example. It is to beexpressly understood, however, that the drawing is for the purpose ofillustration and description only and does not dene limitations of theinvention.

In the drawing:

FIG. l is a schematic diagram indicating the two modes of operation ofthe circulator in accordance with the present invention; and

FIG. 2 represents a typical nonreciprocal wave guide junction inaccordance with the invention.

3,079,570 Patented Feb. 26, 1953 With reference to the drawings, FIG. 1is a diagram` of a three-terminal circulator. The lines A, B and C eachrepresent one terminal of the circulator. In the operation or" acirculator, energy applied to one terminal is coupled to a secondterminal and energy applied to the second terminal is coupled to a thirdterminal, rather than back to the rst terminal as would be the case fora reciprocal structure. For a three-terminal circulator, energy appliedto the third terminal is coupled back to the first'terr'ninal.

Normal circulator action is indicated by the outer arrows designated 12in FiG. l. In accordance with Mode I operation, therefore, microwaveenergy is circulated between terminals A, B and C. When the circulatorof the present invention is switched, however, it operates in accordancewith arrows 14 which designate Mode II. In the case of Mode II, energyapplied to terminal A is` coupled to terminal C; energy applied toterminal C iS,4 routed to terminal B and microwave signals applied toterminal B are circulated back to terminal A. Thus, the circulator maybe switched between Modes I andI II aS developed below.

FIG. 2 shows an apparatus for implementing the Circulator structureshown in FIG. l. In the structure of FIG. 2, a principal wave guide 1,6has a branch wave guide 1S coupled to it at one of the narrower sidewalls of wave guide 16. Within wave guide 16 a cylinder of ferritematerial 29 is mounted in position by a block 22 of po-lyfoam. Thepolyfoam has a very low dielectric constant so that it will support thecylinder 20 without materially interfering with the propagation ofelectromagnetic waves.

In one representative example, the wave guide crossse'ction was one inchby two inches in cross-section, and the ferrite cylinder 20 was mountedin wave guide 16 directly opposite the branch wave guide 18. The ferritecylinder had an outer diameter of one-half inch, an inner diameter ofthree-sixteenths inch, and was three-quarters inch long. The ferritecylinder was centered between the upper and lower broad walls of thewave guide 16 and was located approximately one-sixteenth inch from theback wall of wave guide 16.

The cylinder of ferrite 20 must be magnetized in order to providenonreciprocal coupling between the three terminals A, B and C. In theexample shown in FIG. 2, this is accomplished by the single turn 24 ofinsulated Wire which extends through the cylinder 20. The pulse source26 supplies signals of opposite polarity to the wire 24 to change thedirection of cylindrical peripheral magnetization of the cylinder 2G.When biased in one direction, the microwave energy from wave guide A wascoupled directly to Wave guide output C. When the ferrite cylinder 2i)was magnetized in the opposite peripheral direction, however, microwaveenergy applied to the wave guide A was coupled to output B.

Good energy transfer was obtained between the wave guides which wereintercoupled, and a high degree of isolation of the de-energized waveguide was obtained with this geometry. Specifically, the junctionoperated over a live percent frequency band centered at 5550 megacyclesper second with an insertion loss of less than onehalf of one decibel,and isolation exceeding twenty decibels. These results were obtained inboth switching states, with ve amperes of switching current beingapplied successively, in opposite directions, through a single turn ofNo. 19 wire.

The cylinder 20 is advantageously fabricated from ferrite materialhaving a moderately square hysteresis loop. ri`he many known microwaveferrites having this desired characteristic include the magnesiummanganese ferrites. When these materials are used, followingmagnetization, a high magnetic field strength is retained in thecylinder 23. It is therefore not necessary to have a continued floweerdere of current in the winding 24. When lower speeds of switching ofthe cylinder 2t) may be tolerated, several turns of wire may be passedthrough the cylinder 2i).

It is to be understood that the above-described arrangements areillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention. Thus, byway of example, and not of limitation, the ferrite element may be of arectangular, oval, or square cross-section with a hole through it; and aferrite element of any of these various configurations may be employedas the nonreciprocal element, in a junction having other forms than thatshown in the drawings associated with the present specification. Thus,wave guide junctions of many known forms, such as those disclosed in theSouthworth text cited above, may be adapted for nonreciprocal switchingpurposes by the addition of an apertured ferromagnetic element. Suitablematching and tapering constructions may also be employed in the practiceof the present invention. Accordingly, from the foregoing remarks, it isto be understood that the present invention is to be limited .only bythe spirit and scope of the appended claim.

What is claimed is:

A pulse operated microwave switching device comprising:

a T-waveguide junction consisting of first and second waveguide sectionsof equally dirnensioned rectangular cross section, with broad and narrowwalls, said sections being interconnected at right angles to one anotherwith the first waveguide at one end thereof being connected to thesecond waveguide by an opening in one of the narrow walls of the secondwaveguide corresponding in dimension with the cross Sectional area ofthe first waveguide, the other end of the rst waveguide sectionproviding an input port to receive an input signal and the opposite endsof the second waveguide section selectively providing output ports ofthe microwave switch,

an elongated hollow ferrite member mounted within said second waveguidewith its longitudinal axis generally parallel to the central axis of thesecond waveguide but offset therefrom,

is'ta said ferrite member being disposed adjacent the other narrow wallof the second waveguide section and "being symmetrically disposed withrespect tothe central axis of the rst waveguide section,

said ferrite member having a high remanent magnetization and adapted tobe permanently magnetized at a level close to its saturation levels,

a conductor extending through said hollow ferrite member,

insulated conductor means passing through the narrow wall of the secondwaveguide section that are located proximate to the ferrite member andbeing electrically connected to the conductor within said ferrite memberto provide a continuous electrical circuit therethrough,

said insulated electrical conductor means being energizable by pulseproducing means located external to second waveguide section toselectively apply electrical pulses of opposite polarity thereto toreverse the magnetic polarization of said ferrite member, whereby eachpulse permanently magnetizes the ferrite in a direction controlled byits polarity,

said ferrite member being exclusively magnetized by said pulsesindependently of any other magnetizing source,

means for supporting said ferrite member within said References Cited inthe le of this patent UNITED STATES PATENTS 2,849,683 Miller Aug. 26,1958 OTHER REFERENCES Swanson et al.: 8 IRE WESCON Convention Record,Pant 1, pages l5l-156.

